Verified human-to-human transmission of an animal or human-animal reassortant virus causes community-level outbreaks in at least two countries in one WHO region, and at least one country in a different WHO region.

As of 5/4/09, the world stood at pandemic alert level 5.

Historically, influenza pandemics occur every 30 – 40 years. The last one was in 1968, which leads some to say we're due for another outbreak.

Current epidemiological models project that a pandemic today could cause 2 – 7.4 million deaths around the world. (The current H1N1 outbreak is not currently expected to cause this level of illness or death.) Were an outbreak of that scale to happen, we could expect:

The virus to spread very quickly due to the high level of global traffic

A several-month wait for a vaccine to become available

A shortage of vaccines, antiviral drugs, and antibiotics

Overwhelmed medical facilities

Widespread illness that could cause shortages of people to perform essential community services.

With consequences like that on the line, WHO maintains more than 120 National Influenza Centers in 90 countries to monitor flu activity and isolate viruses in every region of the world. A rapid response is our best defense against the flu.